Problem

Youclimbthelastfewrungsoftheladderandstepinside.“Wow,isthiscool!”Yourfriendisrightbehindyou.“Itoldyou so.”


It’syourfirsttimeinyourfriend’stree house,andwhatasweetsetup.Ithasjustabouteverythingyoucouldwantinabackyardhideaway—twocomfychairs,atable,abookshelf,games,evena TV.


Youplopdowninachairandlookaround.Thenyourealizesomething.“I’mhungry.Gotanyfooduphere?”“Oh,IknewIforgotsomething,”yourfriend says.


Justthen,yourfriend’sgrandmothercomesoutofthehousecarryingtwolunch bags.


“Yay,Grandma,youreadourminds!Now,ifonlytherewasawaytogetthebagsuphere.”

“Hmm . . .”Grandmastaresatathickbranchnearthedoorwayofthetreehouse.“Ihaveanidea.I’llberight back.”


Solution

Afewminuteslater,Grandmacomesbackwitharopeandabucket.“What’sthatfor?”yourfriendasks.“You’llsee,”Grandmasaysasshetiesabigknotinoneendofthe rope.


Sheswingstheknottedendafewtimesandletsitfly.Theropesailsoverthebranch.Theknotdanglesjustafewfeetabovetheground.Grandmaundoestheknotandtiestheendtothebucket handle.


“Oh,Igetit!”yousay.“Whatagreatidea!”Grandmaplacesthelunchbagsinthebucketandpullstheotherendoftherope.Witheachpull,thebucketrisesclosertothetree housedoor.Atthetop,it’seasytoreachoutandgrabthebucket. . . andlunch.Now,thetree houseisperfect.Itevenhasafooddelivery system!

It's Simple

HowwasGrandmaabletodeliverfoodtoyouandyourfriendwithoutclimbingtheladder?Theansweris“simple.”Sheusedtheropeandthebranchasa simplemachine.Likeallmachines,simplemachineshelpusdojobs,usuallybymovingthingsfaster,farther,orinaneasier way.


Simplemachineshavenomorethanafewparts.Infact,somearemadeofonlyonepart.Theycanbecombinedinendlesswaystoaccomplishtasks.Buthowcanaropeandabranchbea machine?

IntheGroove

Well,basedontheheadlineofthisarticle,youprobablyknowtheropeandbranchformeda pulley.Apulleyisawheelwithacordwrappedaroundit.Thecordmightbeastring,arope,achain,orevenasteelcable.Usuallythecordfitsinagroovearoundtherimofthewheel.Thatway,thecorddoesn’tslipout.Thewheelturnsfreelyasthecordispulledthroughthe groove.


Thebranchdoesn’thaveagroove,anditcertainlydoesn’tturnlikeawheel,buttheideaisthesame.WhenGrandmapulleddownononeendoftherope,theotherend,withthebucketattached,movedup.That’sonewayapulleymakesiteasiertoliftobjects.Itchangesthedirectionofa ​​​​​​​force.


Aflagpoleworksthesameway.Aropeisloopedthroughapulleyatthetopofthepole.Toraisetheflag,youattachittoonesideoftheropeandpulldownontheotherside.Theflaggoes up!


Likeanysimplemachine,apulleydoesn’tdotheworkforyou.Toraisetheflag,youhavetopullwithacertainamountofforce.Thepulleydoesn’tincreaseyourforce.Itjustchangesitsdirection.Butthat’saloteasierthanclimbingupthepole,tyingtheflagatthetop,andthenslidingdown again.

Howtoraiseaflagwithapulley

1

Pulldownonthisendofthe rope.

2

Theropemovesthroughthe pulley.

3

Theflagmovesupwiththisendofthe rope.